diff --git a/conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureEnums.java b/conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureEnums.java
index a0a307aa3..d4897a3d2 100644
--- a/conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureEnums.java
+++ b/conjure-lib/src/main/java/com/palantir/conjure/java/lib/internal/ConjureEnums.java
@@ -18,20 +18,12 @@
 
 import com.palantir.logsafe.UnsafeArg;
 import com.palantir.logsafe.exceptions.SafeIllegalArgumentException;
-import java.util.BitSet;
 
 /**
  * Internal utility functions for conjure enum types.
  */
 public final class ConjureEnums {
 
-    private static final BitSet allowedCharacters = new BitSet();
-
-    static {
-        allowedCharacters.set('A', 'Z' + 1);
-        allowedCharacters.set('_');
-    }
-
     private ConjureEnums() {
         // cannot instantiate
     }
@@ -41,12 +33,16 @@ public static void validate(String value) {
             throw new SafeIllegalArgumentException("Enum values must not be empty");
         }
 
-        final int length = value.length();
+        int length = value.length();
         for (int index = 0; index < length; index++) {
-            if (!allowedCharacters.get(value.charAt(index))) {
+            if (!isAllowedCharacter(value.charAt(index))) {
                 throw new SafeIllegalArgumentException("Enum values must use SCREAMING_SNAKE_CASE",
                         UnsafeArg.of("value", value));
             }
         }
     }
+
+    private static boolean isAllowedCharacter(char character) {
+        return (character >= 'A' && character <= 'Z') || character == '_';
+    }
 }